I. Field of the Invention
The present invention generally relates to wireless communications, and more specifically to a wireless portable telephone that selects a single voice service option from among a plurality of voice service options supported by the portable phone.
II. Related Art
Wireless portable and mobile telephones have become commonplace as an accepted addition to or replacement for conventional landline telephone systems. Wireless portable or mobile telephones offer the convenience of wireless communications from almost any location in the country or the world.
Wireless telephones, which include both satellite and cellular phones, are communications devices that function in a wireless environment. There are three basic types of wireless telephones. Portable phones are typically small, handheld devices that can be carried on the person. Mobile phones are typically mounted in a vehicle; they have a base unit or cradle that is fixedly mounted to the vehicle, usually inside the passenger compartment, and a handset that is connected to the base unit or cradle by a wire. A fixed wireless phone is usually mounted in a single location. Any of these types of phones can be operated over a terrestrial cellular network or over a satellite communications network. Some wireless phones are capable of operating over both cellular and satellite systems.
Wired phones are those connected directly to a wireline phone system by wires. Wired phones are the typical standard phones found in what is called POTS (Plain Old Telephone Systems). Telephones that operate over short range wireless links, such as portable phones that are used in the home or small business environment, and which transmit to and receive signals from a single fixed base station or unit over a short range (for example, several hundred to a thousand meters), where the base unit is directly connected to a wireline communications network, are not considered wireless phones for purposes of this disclosure. Such single station, short range wireless phones are called "cordless phones" and are considered to fall into the category of standard wireline phones (that is, phones connected to the communications network by wires).
In any given geographic region there may be a number of wireless telephone service providers, each operating their own wireless telephone network, which may cover an entire country or just a region. Each wireless telephone service provider may support different voice service options. For example, in a code division multiple access (CDMA) cellular telephone network, the voice service options can include an IS-96-A voice service option (hereafter "8K voice service option"), an IS-733 voice service option (hereafter "13K voice service option"), and an IS-127 voice service option (hereafter "EVRC voice service option"). Each of the foregoing IS specifications is available from the Telecommunication Industry Association (2001 Pennsylvania Avenue, Suite 800, Washington, D.C. 20006). Today, the EVRC voice service option is the preferred voice service option because of its high quality and low bandwidth.
Problems arise when not all of the service providers support the same voice service options. For example, if service provider Y offers the EVRC voice service option, but service provider X does not, then when a customer of Y travels into X's region, the customer may not be able to make or receive phone calls. This will be the case when the customer's wireless phone is configured for the EVRC voice service option and X's network does not support voice service option negotiation.
What is desired, therefore, is a subscriber unit that supports multiple voice service options and can intelligently select a voice service option when originating and receiving a call.